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Although atrial fibrillation (AF) is well known to be associated with an increase in the risk of stroke and coronary heart disease, a similar association with sudden cardiac death (SCD) has been suspected but not demonstrated in the past. Now a new study examing data from two large population studies offers evidence that AF is also an independent risk factor for SCD.

In a paper published in JAMA Internal Medicine (formerly Archives of Internal Medicine), Lin Chen and colleagues analyzed data from from 15,439 participants in the Atherosclerosis Risk in Communities (ARIC) Study and 5,479 participants in the Cardiovascular Health Study (CHS). The analysis shows that AF patients were at significantly elevated risk for SCD. The increase in SCD was roughly similar to the expected increase in nonsudden cardiac death.

SCD hazard ratio adjusted for risk factors:

ARIC: 3.26 (CI 2.17-4.91), p<.001

CHS: 2.14 CI(1.60-2.87), p <.001

Combined: 2.47 (1.95-3.13), p<.001

The authors concluded that their finding, if confirmed, "adds to our evolving understanding that AF is not a benign condition. Not only does AF predispose to stroke, heart failure, and death, but the arrhythmia per se may increase the risk of death from ventricular tachyarrhythmias."

In an invited commentary, Kyndaron Reinier and Sumeet Chugh write that despite the statistical adjustments the study may have been unable to demonstrate a cause-and-effect relationship between AF and SCD, since the findings "may be due to shared risk factors." They also point out that some of the SCD cases may have been really caused by a cerebrovascular accident.

They urge caution regarding attempts to apply the findings of the study to clinical practice:

"...it is important that we are cautious about extending these findings into the clinical domain. Until such time that a causal association is confirmed between AF and SCD, it is difficult for these results to influence clinical management of AF or SCD. Whether it is control of the heart rate, control of the rhythm, or stroke prophylaxis, present management of the patient with AF should be governed largely by current evidence-based guidelines aimed at reduction of AF symptoms and hospitalization and the need to minimize risk of future cerebrovascular accidents."